Our current understanding of the sources of pain and hence disability in knee osteoarthritis (OA) is limited. Previous research has concentrated primarily on tibiofemoral (TF) joints and has shown a poor correlation between structural change and both pain and disability. Relatively little heed has been paid to the patellofemoral (PF) joint, despite suggestions that it may be strongly correlated with lower extremity disability, and that assessment of the PF joint in knee OA provides a clearer explanation for knee pain. Whilst good information is available for TF OA, the epidemiology of patellofemoral OA remains unclear. Moreover current data suggest that the risk factors associated with disease are different for PF OA and TF OA. The contribution of risk factors likely unique to the PF joint including the relationship of quadriceps strength, hamstring quadriceps muscle imbalance, muscle mass, patella malalignment and femur length to PF OA is unknown. This project will take advantage of already collected data from a large-scale longitudinal study that incorporates extensive evaluations of knee pain and disability and serial knee MRI's and x-rays on participants; to address one overall specific aim. Using longitudinal data (including serial MRI) to explore PF cartilage loss, and risk factors for PF OA. In this project we will evaluate PF cartilage loss and development of this same PF cartilage loss associated with symptoms.